How to get rid of presumably limescale from your pool ?

Terry Keep's picture

When we bought our place 5-6 years ago, it came with a pool ...(yippee I thought) but I didn't realise how expensive it was to look after a large pond in the garden.


Knowing very little about swimming pools except they look good and inviting (well on the telly they do), I was amazed at the number of issues we have had.


For the last 2-3 years we have had to replace the whole water as this gives me a chance to karture the pool walls and floor. It appears that lime scale is on the pool and that also appears to give algae and things something to hang on to so you can not 'brush' it off. The karturing doesn't appear to get it all off (or maybe I get bored of karturing for a whole day !)


So how can you remove the lime scale and stop it coming back with draining the pool and not having a massive water softener attached !

John Withall's picture

Welcome Terry,

It is all a question of water balance.  France is a big area and some of it has very hard water like yours and a somewhat like mine.  What you really don't want to be doing is changing the water every year for fresh water with yet more hardness to deposit.  Sorry, it's better to treat the water you have and maintain that at the correct levels.  That requires testing and accurate testing.  To reduce the hardness you could filter through a reverse osmosis filter but you would need a big one!  You could use a water softner which is full of salt which softens via and ion exchange so sodium replaces the calcium (that is the scale) similar to why some report salt water chlorine pools as feeling softer.  Or counter the hardness with an increase in the acid level. That would reduce the pH which would then need to be raised without the addition of chemicals or you'll end up where you started.  Over a period of days you will then get the hardness lower and the pH stable at a point where the water is neither corrosive or scaling. At that point you want to keep that water in the pool for as long as you can and then maintenance will be so much easier and cheaper.

That is a simplified version but it is what needs to be done to balance the pool and we can look at the alcalinity levels too as in a tiled pool it is important to get the levels corrrect or the grout gets erroded over time as apposed to scale forming.

Roger Thomas's picture

I too live in a hard water area but do not suffer from scale, When the pool was installed (six years ago) the pool man added a product called anti-calc (?) to the pool followed by the other chemicals to give the correct Ph. Its only during the high summer that we need to add any water at all, during the winter its usually a case that the pool overflows with lovely soft rain water. If you are having problems with high evaporation then you need to use a cover.

John Withall's picture

Be careful with anti calc, early formulations were often phosphate based and phosphates are like caffine to algae etc.  Later versions tend to be based around Ethylenediaminetetraacetic acid (EDTA) which is a metal sequesterant but can help with water hardness.  EDTA is slowly used up by chlorine breaking it down so requires frequent topping up. As you said Roger better to top up by harvesting the rain water, that will be dirty until filtered and will use more chlorine initally but it is a solution.

Don Duca's picture

After 9 years in this hard water house I just last week had a sophisticated little water filtration system installed by the husband of the woman who runs the local bio. She has been a font of good local information for me and her English is impeccable, which was a big help when I was just starting to learn la langue.

I installed this system in the garage, where the water main enters the house. It is mounted in such a way that should I move, I can turn two valves to bypass the filtration system, remove the system from the wall and take it with me. My reason for installing this system was finally being fed up with limescale build up on everything to do with water... from toilet bowl, robinets, tub, to dishes and laundry. Also lugging in bottled spring water for drinking and cooking was an expensive proposition.

The new system is brilliant. It has two large filter elements. Within these two housings are several different stacked filters. One must be changed annually, while the other is good for two years. They remove everything that we don't want from the whole house water supply. My biggest concerns were calcaire and chlorine. They are now gone. Glasses and dishes now dry spotless and the difference in my skin and hair after shampooing is pretty dramatic. I am seeing great future health benefits, for the dogs too. I think that there will also be benefits from chlorine free water in the kitchen garden and house plants. This will probably also greatly extend water heater life.

Stop treating the symptoms and go straight after the cause.

The system installed ran Euro 1300.00. I estimate that this is about what I was spending per year on bottled water. Water from this filtration system will fill a pool with sparkling clean, lime-free water. The only other pool concern would be algae control. This will solve your pool problem, as well as all of the annoying effects of hard water in the home.

John Withall's picture

As I described earlier a water softener and micro filtration unit will do the job. The softener uses salt to exchange calcium for sodium that doesn't coat everything in lime/chalk.  The filtration system is ultrafine but not as fine as RO. The unit you have will have a specification for it's work load and through put, if that matches the size of the pool then no issues but usually they cannot cope with the volume of a pool. In The USA a colleague has a truck mounted RO rig that he uses to filter just about everything out of the water rather than waste it and he is busy most of the time.

Oh and you don't want a completely lime free pool, that would be very bad, you need just the right amount generally between 100-300ppm

Don Duca's picture

I would think that adding the proper ratio of lime is preferable to removing the results of excess. I do not have a pool so I am certain that people dealing with their issues are far more knowledgeable than I.

Dick Smith's picture

Hi Terry,

My advice would be to go to a local pool company. They will have the advice and products suitable for your area. I presume you are testing chlorine and pH levels. It is a bit early for me to open my pool in Charente-Maritime but I haven't had scale problems in the past and we have very hard water - 28 degrees.

John Withall's picture

Dick the biggest issue facing pool owners IS the local pool company.  I cannot stress enough the rubbish and mis information these people trot out. They have No understanding of how things work and even more a total lack of understanding of the chemistry involved. The whole idea of the SFN pool section is to finally lay to rest some of the nonsense spoken about pools.

Frances Bourne's picture

Whatever you do, you need to make sure the pool is thoroughtly clean first and speaking to a  pool expert (local or otherwise!) is the best way to go about this, as it will depend on whether you have tiles or a liner.

Then you have a choice of water softeners, electronic water conditioners, or other products that are available.  We have a spa pool and used a product called Aquafinesse (there are probably others too), which is environmentally friendly (no chlorine, just the odd Shock treatment), but I do not know whether they have a product available for a large pool - worth a check though as we are big anti-chemical.  However, as we learnt rather quickly and as John said , it is also about the PH levels - if they are right the (spa in our case) pool remains relatively balanced. Most of our neighbours have pools and they do seem to be time consuming (which is why we didn't have one!) and they all have different issues to deal with regarding pool care.  However, I know they all enjoy using it  when the weather is warm!So good luck with getting to grips with it - am sure you will.

John Withall's picture

Ok this may get a little controversial. 

There is an awfully large amount spoken about with people being anti chemical, it means different things to different people but one thing is certain be it pool or spa it contains chemicals it just depends on which ones.

Aquafinesse products are mainly cleansers that breakdown and remove biofilms, from this MSDS you can see that it is mainly Sodium carbonate (or PH + as we call it) and Disodium metasilicate, which is a floculent and clarifyer which helps remove small particles.  The "odd shock" is Chlorine so you have a clean but clorinated pool/spa which is just what we would want but without the higher price tag. Biofilms are more prevalent in spas and hot tubs due to the higher temperatures encouraging bacterial and mould growth so anything that helps with the situation is by way of an insurance policy.  Pools being cooler would not really warrant the extra but it's a personal choice.

Terry Keep's picture

Thanks everyone for the fast responses....

John,

So I understand the bit about not changing the water each year because I am only putting in hard water - but that did let me have a go at the limescale.

So if I read your reply correctly, probably my best option is to put a water softener device in. I have had a quick look around but have not found much except domestic ones for homes not pools.... can you advise ?

Thanks again.

John Withall's picture

Hi Terry,

Before making any recommendations, I really could use a full breakdown of the water. This is preferable to guessing and also monitors the precise levels we are talking about and of course how much we achieve in setting up the pool correctly.  The basics levels we need in order to look at your water issue are:

Total AlkalinityCyanuric acidFree ChlorineTotal ChlorineCalcium HardnessPHVinyl liner or tiled/plasterSize of the pool m3

How is it chlorinated, via chorine, multi action gallets or salt water chlorine production?

What type of filter?

It may seem a lot at this point but your issues can be cured, the pool maintenance will become a lot easier and costs will be manageable.

Roger Thomas's picture

One thing any house wife will tell you is that an application of acid to lime scale will cure the problem. I hope I have understood the problem you have, but if you are running a pool with a water which is hard and alkaline you will get lime scale. conversely a slightly acidic pool will actually dissolve it ( if I've got my chemistry right).

if you post your liner type, water ph (Acid/alkali ) etc as suggested then the true experts here will be able to make recommendations so that you neither have to Kartcher your pool nor buy a water softener nor suffer a poor swim water experience.

Carol Norwell's picture

Replacing all the water is a huge expense as well as a huge undertaking (unless you have a very diddy pool). We had a 10 x 5 metre pool for 18 years....in a hard water area. We didnt have a water softener for the pool water (outside tap) so it was important to make sure the pool PH was kept correct. Weekly testing, use of chlorine or a salt water system, will ensure you dont get calcium buildup. If you close the pool for the winter...it does take some cleaning, used to take us a week or two to get it back to sparkling, and scrubbing the sides with a long handle brush vacuum was a must....our pool was a killer...12ft or nearly 4 metres at the deep end made for very well muscled arms! but once you get it clean, and I mean with the pool full of water...its easy to keep it clean. Most pool owners dont change the water....you shouldnt need to if you keep the chemical balance ok...we used very, very little chemicals...but at one stage had the same water for 10 years....obviously with regular top ups...our pool people told us that was the norm. Enjoy your pool, its worth that bit of effort.

John Withall's picture

Dear Carol,  Whilst I may be a bit scared of your well muscled arms, I must make a correction that neither chlorine or a salt water chlorine generating system prevents calcium build up. There are many people with salt water chlorine generators who take the cell out each spring and soak it in weak acid to de calcify the plates as the build up can be problematic and prevent chlorine being generated.

Calcium hardness, is from the calcium carbonate in the water and whilst it may have an effect on the pH it will quite happily exist at the pH that we use.

I do agree that hanging on to your water once the problem has been sorted is a very important issue and small top up amounts could be from rain water harvested sources.  The pool builders don't make enough use of overflow ports on skimmers which can also be used to collect the excess water from the pool which can of course be reused in the future which saves a fair amount over a season and with hose pipe bans can allow you to keep your pool topped up and running through the summer.

John Withall's picture

Well it looks like we have scared poor Terry away. Was it the talk of testing the water? or not being able to find a bottle of calcium reducer?  Membership has grown to 20 so more people must have taken the covers off by now. It would seem good news though as everyone has stayed quiet so no issues to sort out. All pumps running nicely. 

Carol Norwell's picture

Cant understand then why we never had any calcium build up despite being in a very hard water area...and using a water softener inside the house. We had our pool for 17 plus years...never used anything other than PH balancing substances and chlorine..which we used very little of. We never once had any build up and apart from a sand filter...did nothing other than keep the water going and only changing it a couple of times during that period for pool maintenance.

John Withall's picture

It is never straight forward Carol as to why one pool does this and another just down the road does that.  That's why having a full water analysis is important if you have a problem.  I too have hard water 280ppm calcium hardness and I do not have scale but if a dip strip test is correct (which I doubt) another chap posted he has water 400-450 ppm Calcium hardness, now that's very hard water!

I know in Terry's case he inherited the pool but all things considered a pool costs about the same as a family car, would you trust a mechanic with tools from a 99p shop.  That is the equivalent of using dip strips. Yes you can get away with it but when things go wrong, that is the time when the "how do I put it right" begins.  My BIL won't take any notice and I have one of the best testers on the market, so I don't bother him. He panicks every time his pool goes cloudy just before guests arrive and when he can't cope anymore he empties 90m3 of water and refills. I can't help some people and inlaws are some of those people. LoL

Carol Norwell's picture

wow....now emptying all that water is a step too far. My OH got to the stage of knowing our pool so well, we rarely had a cloudy pool other than when we went on holiday (leaving our poor friends in charge of the pool who used to panic like your BIL)..and on the odd occasion of a very heavy electrical storm which could turn the water cloudy overnight. My OH barely used any chemicals...the minimum of chlorine and it was always crystal clear....missing it as I think about it!

Simon Davison's picture

Hi...a question, perhaps for John with his extensive knowledge to answer? In adding an "anti-calcaire" solution (either phosphate or EDTA based) to the water can you please tell me what is chemically happening, is the excess calcium essentially being precipitated to a solid form to be later removed via filtering/hoovering, basically where does it go?

Paul Dorey's picture

Hi John Thanks in main to your excellent advice, our 'desy'pool has been much easier to maintain over the last couple of years. The ColorQ testing kit has been invaluable to obtain reliable results and a relevant action plan. Just a couple of queries; The plastic test tubes are beginning to become cloudy. Does this affect accuracy, and do you recommend changing them after a 2 or 3 years? The alkalinity and calcium hardness are constantly well below 'ideal' levels. This has no apparent effect on overall water quality. PH always reads between 7.2 - 7.4 and is no bother. I like the idea of 'soft' water anyway (It tastes better!!)Should I be concerned and take action?

John Withall's picture

Hi Paul,

All very good questions!

Yes the test tubes being plastic do go cloudy and fine scratches, this scatters the light source so reading can go off, Replacements tubes are cheap enough, drop me an email and we can sort that out. I did some hunting around for optical quality glass test tubes that would fit but at £75 for 3, I thought I doubt it!

The "ideal" levels, I know the book contains lots of helpful advice but that isn't one of them, well not if you have a vinyl pool. 

Alkalinity in the form of bicarbonate in water is used as a buffer solution. This is to try and keep the water at the correct pH which was originally done to protect concrete/plaster/tiled pool surfaces from degradation by water in the pool.  This doesn't happen in a vinyl pool, the bicarbonate of soda solution in a pool buffers the pH at 8.3, way above what we want. The higher the Alkalinity the stronger the "Pull" to pH 8.3 and the more PH- you need to get it to move.

This is great news for the pool industry, they sell more bicarb (sorry Alkalinity+) and then more pH-  so you can keep adding each in turn what fun, not.

In a vinyl pool you need only enough Alkalinity to stop the pH drifting from 7.2-7.8 if your pH is relatively stable then it's fine, out of interest what is the level?  Mines about 37ppm.

Be warned if you use low Alkalinity as I do it takes a lot less pH- to get the pH to move. Multi action galets could cause the pH to drop slightly using low Alkalinity.

Calcium hardness, some of this is desirable, Calcium being a metal has a + charge and that helps to flocculate - charged particles in the water and then it helps the filter to collect those (Only if your filter is fine enough) otherwise it just goes around and around so nothing to worry about in a vinyl pool.

Hope that helps